linux-kernel - Re: [PATCH v5 4/8] char: rpmb: provide a user space interface

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Message-ID: <20160904202029.GB31115@amd>
Date:   Sun, 4 Sep 2016 22:20:29 +0200
From:   Pavel Machek <pavel@....cz>
To:     "Winkler, Tomas" <tomas.winkler@...el.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        "Hunter, Adrian" <adrian.hunter@...el.com>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Vinayak Holikatti <vinholikatti@...il.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arve Hj?nnev?g <arve@...roid.com>,
        Michael Ryleev <gmar@...gle.com>,
        Joao Pinto <Joao.Pinto@...opsys.com>,
        Christoph Hellwig <hch@....de>,
        Yaniv Gardi <ygardi@...eaurora.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>
Subject: Re: [PATCH v5 4/8] char: rpmb: provide a user space interface

On Sun 2016-09-04 11:35:33, Winkler, Tomas wrote:
> 
> > On Thu, Sep 01, 2016 at 08:05:26PM +0000, Winkler, Tomas wrote:
> > >
> > > >
> > > > On Sun, Aug 07, 2016 at 09:44:03AM +0000, Winkler, Tomas wrote:
> > > > > >
> > > > > > On Mon 2016-07-18 23:27:49, Tomas Winkler wrote:
> > > > > > > The user space API is achieved via two synchronous IOCTL.
> > > > > >
> > > > > > IOCTLs?
> > > > >
> > > > > Will fix
> > > > >
> > > > > > > Simplified one, RPMB_IOC_REQ_CMD, were read result cycles is
> > > > > > performed
> > > > > > > by the framework on behalf the user and second,
> > > > > > > RPMB_IOC_SEQ_CMD
> > > > > > where
> > > > > > > the whole RPMB sequence including RESULT_READ is supplied by
> > > > > > > the
> > > > caller.
> > > > > > > The latter is intended for  easier adjusting  of the
> > > > > > > applications that use MMC_IOC_MULTI_CMD ioctl.
> > > > > >
> > > > > > Why "  "?
> > > > > Not sure I there is enough clue in your question.
> > > > > >
> > > > > > >
> > > > > > > Signed-off-by: Tomas Winkler <tomas.winkler@...el.com>
> > > > > >
> > > > > > > +
> > > > > > > +static long rpmb_ioctl(struct file *fp, unsigned int cmd,
> > > > > > > +unsigned long arg) {
> > > > > > > +	return __rpmb_ioctl(fp, cmd, (void __user *)arg); }
> > > > > > > +
> > > > > > > +#ifdef CONFIG_COMPAT
> > > > > > > +static long rpmb_compat_ioctl(struct file *fp, unsigned int cmd,
> > > > > > > +			      unsigned long arg)
> > > > > > > +{
> > > > > > > +	return	__rpmb_ioctl(fp, cmd, compat_ptr(arg));
> > > > > > > +}
> > > > > > > +#endif /* CONFIG_COMPAT */
> > > > > >
> > > > > > Description of the ioctl is missing,
> > > > > Will add.
> > > > >
> > > > > and it should certainly be designed in a way
> > > > > > that it does not need compat support.
> > > > >
> > > > > The compat_ioctl handler just casts the compat_ptr, I believe this
> > > > > should be done unless the ioctl is globaly registered in
> > > > > fs/compat_ioctl.c, but I might be wrong.
> > > >
> > > > You shouldn't need a compat ioctl for anything new that is added,
> > > > unless your api is really messed up.  Please test to be sure, and
> > > > not use a compat ioctl at all, it isn't that hard to do.
> > >
> > > compat_ioctl is called anyhow when CONFIG_COMPAT is set, there is no
> > > way around it, or I'm missing something?  Actually there is no more
> > > than that for the COMPAT support in this code.
> > 
> > If you don't provide a compat_ioctl() all should be fine, right?
> 
> No,  this doesn't work the driver has to provide compat_ioctl
> 
> You would expect something like
> if (!f.file->f_op->compat_ioctl) {
>                         error = f_op->f.file->f_op->unlocked_ioctl((f.file, cmd, compat_ptr(arg))
> }
> But there is no such code under  fs/compat_ioctl.c 
> 
> The translation has to implemented by the device driver or registered  directly in fs/compat_ioct.c in do_ioctl_trans or ioctl_pointer[]
> 
> If compat_ioct is not provided the application is receiving
> : ioctl failure -1: Inappropriate ioctl for device

Care to submit a patch? We should not really have to include
compat_ioctl support if it is already compatible...

Or maybe better provide empty function drivers can fill in when
compatible...?

									Pavel

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